Twenty foreign tourists including Britons, South Africans and an Indian national have been arrested in northern China, according to reports by Britain's Foreign Office and a South African charity, on suspicion some had ties to a "terror group."

China has agreed to release 11 of the tourists, but the rest will continue to be held without charge at a detention center in Inner Mongolia, said the South African charity, Gift of the Givers Foundation.

Chinese authorities said some of those arrested had been watching propaganda videos from a banned group in their hotel room, the charity added in its statement.

Five South Africans, three Britons and one Indian national make up the nine being held, it said.

"Consular staff have visited the group to provide assistance and we are liaising with Chinese authorities," a British Foreign Office spokesman said.

The Chinese Foreign Ministry and the South African embassy did not immediately respond to a request for comment. An Indian embassy spokesman said he had no information on the matter.

Chinese law enforcement authorities could not be immediately reached for comment.

The group was on a 47-day tour of the country when they were detained at an airport in the Inner Mongolian city of Erdos. Their tour operator realized something had gone "horribly wrong" on Sunday, two days later, the foundation said, when he hadn't heard from them.

"These individuals have no terror links, no criminal record in their country," said Gift of the Givers, which has negotiated hostage releases.

"The families thank the South African government for their unwavering support and call upon the Chinese government to release the detainees immediately."

Several of those detained are relatives of Shameel Joosub, chief executive of telecoms company Vodacom Group Ltd., the charity added.